Secondary batteries such as lithium ion secondary batteries have characteristics such as compact size, light weight, high energy-density, and the ability to be repeatedly charged and discharged, and are used in a wide variety of applications. Consequently, in recent years, studies have been made to improve battery members such as electrodes for the purpose of achieving even higher secondary battery performance.
Battery members such as electrodes (positive electrodes and negative electrodes) for use in lithium ion secondary batteries may be formed by using a binder (binding material) in order to bind components contained in such a battery member to one another or in order to bind these components to a substrate (for example, a current collector). In one specific example, an electrode of a lithium ion secondary battery generally includes a current collector and an electrode mixed material layer formed on the current collector. The electrode mixed material layer is for example formed by applying, onto the current collector, a slurry composition in which an electrode active material, a binder composition, and, as necessary, a conductive material and so forth are dispersed in a dispersion medium, and by drying the applied slurry composition.
In recent years, there have been attempts to improve binder compositions and slurry compositions used in formation of battery members such as described above in order to further improve secondary battery performance.
In one specific example, PTL 1 reports that dispersibility of an electrode active material, and also rate characteristics and cycle characteristics of a lithium ion secondary battery, can be improved by producing an electrode for the lithium ion secondary battery using a binder composition that contains, as a binding material, a copolymer including a cationic group such as a quaternary ammonium salt group, a sulfonium salt group, or a phosphonium salt group. In PTL 1, various chlorides are used as cationic group-containing monomers that can be used in preparation of the aforementioned cationic group-containing copolymer.